Feast your eyes on the "Mini Lisa," recently created by a team of researchers at Georgia tech. While it looks here to be a decent size, it in fact measures just 30-microns thick – a little under half the width of the average human hair:

The tiny masterpiece was made through a process called ThermoChemical NanoLithography: with a heated cantilever, a tiny device that can accurately apply heat to a surface, the researchers induced heat-based chemical reactions on a surface. The more heat they applied, the lighter a shade of gray the picture became in that area. So with each area acting like the pixel in an image, the researchers applied different amounts of heat at different spots, until they created a gray-scale version of da Vinci's famed painting.